A ball bearing assembly process includes a grease sealing process of arranging a plurality of balls in an annular space between an outer ring and an inner ring and then supplying grease into the annular gap. In the grease sealing process, a predetermined amount of grease is supplied into the annular space. Generally, in the grease sealing process, a grease nozzle which discharges the grease pneumatically transported by a pump from small holes or slits arranged in a circular ring shape is widely used (for example, refer to Patent Documents 1 and 2).
FIGS. 10A and 10B show an example of a configuration of the grease nozzle. FIG. 10A is an outward perspective view of the grease nozzle and FIG. 10B is an axial sectional view of the grease nozzle. In a grease nozzle 500, a plurality of nozzle holes 502 corresponding to grease injection places of a ball bearing is arranged in a circular ring shape. When sealing the grease in the ball bearing by using the grease nozzle 500, each nozzle hole 502 of the grease nozzle 500 is first made to face an annular space between an inner ring and an outer ring of the ball bearing and then a pump (not shown) connected to the grease nozzle 500 is driven at that state. Thereby, the grease is discharged from each nozzle hole 502, so that the grease is filled in the annular space between the inner ring and the outer ring of the ball bearing, particular in areas between pockets of a retainer.